1. Technical Field
The present invention relates to a telephony system comprising terminal devices and a connection control device for establishing a call connection between the terminal devices based on a connection request received from the terminal device, in which, when the connection control device is in a congested state, newly received connection requests are stored in the order they are received and the wait time until a connection becomes certainly available is notified, and also relates to a connection control method, a connection control device for use in the telephony system, and a recording medium storing a computer program for causing a computer to function as a connection control device.
2. Description of Related Art
In the case where the amount of calling increases temporarily, such as when a disaster happens or when ticket reservation is started, a switchboard may fall into a congested state in which call processing is delayed due to a lack of hardware resources required for call processing to establish call connections, and calls are hard to be established. Considering such a situation, the switchboard is generally designed to give a message such as “A connection is hard to be established.” to the caller and reject the establishment of a call connection if a new incoming call is detected when the amount of calling became larger than a predetermined threshold value.
However, if only a message informing that a call is hard to be established is simply given, the callers who were rejected for establishing call connections often repeat calling again, and therefore the congested state of the switchboard is not solved. Moreover, since the callers are unable to know when calls become available, they may further repeat calling, and hence the congested state is not solved.
During the congested state, a decision as to whether a call connection is established or the establishment of a call connection is rejected in response to an incoming call is made based not on the order the incoming call was detected by the switchboard, but on the detection timing, and therefore the callers may feel unfairness such as unequal opportunity to establish calls.
Hence, there is disclosed a technique to solve the problem of callers' unequal opportunity to establish calls by classifying subscribers according to mobile communication systems and further assigning a priority order to each class to differentiate the connection available time and limit the connection time based on the priority orders (Japanese Patent Application Laid-Open No. 09-130855 (1997)).
There is also disclosed a technique to solve the unequal connection opportunity by storing the phone number of a caller of an incoming call which is not automatically responded because all operators are busy in a system, such as a call center for ticket reservation, in which the operators are supposed to respond to incoming calls, notifying the caller of an average wait time, and calling back the stored caller's number when an operator is free (Japanese Patent Application Laid-Open No. 10-093717 (1998)).
As a technique of limiting connections to solve the congested state, there is disclosed a technique in which, when a switchboard accommodating a destination telephone terminal device is in a congested state, the message of the caller and the phone number of the called party are stored in a switchboard accommodating the source telephone terminal device without transmitting an incoming call to the destination switchboard, and after solving the congested state in the destination switchboard, the presence of the stored message is notified and the message is transferred to the destination telephone terminal device (Japanese Patent Application Laid-Open No. 10-093708 (1998)).
Moreover, there is disclosed a technique capable of completing a reservation within a short processing time by separately providing a reservation line for receiving reservations to establish call connections, receiving an incoming call by a terminal device through the reservation line when a congested state occurs, making a reservation to store the caller number of the caller of the received incoming call and the connection available time, and notifying the caller of the connection available time, and also capable of solving the congested state by preventing the caller from repeatedly calling until the connection available time (Japanese Patent Application Laid-Open No. 64-089646 (1989)).
There is also disclosed a technique for solving the congested state by determining and limiting the connection time when the congested state occurs, forcefully disconnecting an established call connection exceeding the connection time by a switchboard, rejecting the establishment of a call connection for a newly detected incoming call, and notifying the caller of the connection available time estimated based on statistics in case of rejection (Japanese Patent Application Laid-Open No. 2002-232563).
By the way, with the advancement of VoIP (Voice over Internet Protocol) technique capable of converting voice into digital data and exchanging data over a packet switched network, services for providing an IP (Internet Protocol) telephony system, which enables a call by establishing a call connection through a packet switched network, such as the Internet, instead of a conventional fixed telephone network, have been spread.
The IP telephony system enables a call by establishing a call connection when a terminal device, such as a computer having the function of converting voice into digital data or a router, and a connection control device for establishing a call connection between terminal devices exchange data based on Session Initiation Protocol (hereinafter referred to as SIP). SIP is rules which define a method of describing a message represented by text data and a message exchange method. By exchanging messages based on SIP between the terminal devices and the connection control device, services such as the establishment of a call connection or error notice are realized.